This invention relates generally to optical multiplexing/demultiplexing and more particularly to an optical device capable of processing different wavelength channels in multiple bands of a wavelength window.
The rapid adoption of the Internet has resulted in a need to provide large amounts of bandwidth over long distances. To accomplish this optical networks have been deployed all over the world. The amount of information that a single fiber optic cable can carry is typically boosted using wavelength division multiplexing (WDM). This technique allows many different wavelengths of light to travel over the same fiber. Many different DWDM technologies have been developed, including integrated waveguide demultiplexers based on phased array waveguide gratings (AWG) and etched echelle grating-on-a-chip spectrometers. The integrated devices have many advantages such as compactness, reliability, reduced fabrication and packaging costs, and potential monolithic integration with active devices of different functionalities. The wavelength range of a WDM system is determined by the optical amplifiers used in the transmission line. Currently the most commonly used amplifiers are erbium-doped fiber amplifiers (EDFA). The wavelength windows are from 1530 nm to 1565 nm (C-band) and from 1570 nm to 1610 nm (L-band). Each of the wavelength windows can accommodate about 40 channels with 100 GHz (xcx9c0.8 nm) spacing, or 80 channels with 50 GHz (xcx9c0.4nm) spacing.
For many network applications, especially for metropolitan networks, it is desirable that the system be scalable, for instance a small number of channels are added/dropped at a node initially but that number may be increased at a later time together with the total number of channels in the system, as demand on the network increases. Such a scalable system requires many multiplexers and demultiplexers of a small channel count, such as 4, 8, and 16-channel devices. Each of the devices operates within a narrow wavelength band of several nanometers. A large number of different components with different operating wavelength bands are required to cover the whole wavelength window of the EDFA. For example, for a system designed with 4-channel 100 GHz spacing or 8-channel 50 GHz spacing as a unit, the operating wavelength band of each device is about 3.2 nm. At least ten different multiplexers and demultiplexers are required to cover each of the EDFA windows. Therefore, the system providers and component suppliers need to maintain a large inventory to stock each of the different parts. The cost for maintaining such a large inventory is very high.
It would be very beneficial to produce a multiplexer/demultiplexer component featuring the capability of operating over more than one band. Even if the device should end up being used on only a single band then a benefit still exists because the organizations that need to maintain inventories of these parts will be able to use the same part for any band instead of being forced to stock different parts for each band. It also simplifies the manufacturing and assembly processes for both system and component suppliers because the number of different components is reduced.
It is an object of the invention to provide a waveguide grating based component capable of performing multiplexing or demultiplexing function in multiple wavelength bands.
In accordance with the invention there is provided an optical device for use in an optical network having a predetermined application wavelength window comprising:
an input port for receiving a multiplexed optical signal including optical signals within each of a plurality of wavelength channels having a predetermined channel spacing within any one of a plurality of non-overlapping wavelength bands within said application wavelength window;
a plurality of output ports;
a wavelength dispersive element for separating the multiplexed optical signal received at the input port in dependence upon wavelength to provide a channelised signal to each of the output ports;
wherein the device is for operation within any one and only one of a plurality of non-overlapping wavelength bands at a same time within said application wavelength window and wherein an optical signal corresponding to a first optical channel within any one of said plurality of non-overlapping wavelength bands is provided to a first output port, a second optical signal corresponding to a second optical channel within any one of said plurality of non-overlapping wavelength bands is provided to a second output port, and an n-th optical signal corresponding to an n-th optical channel within any one of said plurality of non-overlapping wavelength bands is provided to the n-th optical output port.
In accordance with another embodiment of the invention there is provided an optical network having a predetermined application wavelength window comprising:
a plurality of optical band add-drop nodes each comprising
a demultiplexing device supporting multiple wavelength bands within the application wavelength window including:
an input port for receiving a multiplexed optical signal including optical signals within each of a plurality of wavelength channels having a predetermined channel spacing within an add-drop wavelength band corresponding to any one of a plurality of non-overlapping wavelength bands within the application wavelength window;
at least three output ports; and
a wavelength dispersive element for separating the multiplexed optical signal received at the input port in dependence upon wavelength to provide a channelised signal to each of the at least three output ports,
a multiplexing device supporting multiple wavelength bands within the application wavelength window including:
an output port for receiving a multiplexed optical signal including optical signals within each of a plurality of wavelength channels having a predetermined channel spacing within a same add-drop wavelength band corresponding to any one of a plurality of non-overlapping wavelength bands within the application wavelength window;
at least three input ports; and
a wavelength dispersive element for combining the channelised optical signals received at the input ports in dependence upon wavelength to provide a multiplexed signal to the output port,
a first optical band pass filter for separating optical channels within said add-drop wavelength band from those of other wavelength bands and for providing optical signals within the optical wavelength channels within the add-drop wavelength band to the input port of the demultiplexing device; and,
a second optical band pass filter for receiving optical signals within other wavelength bands from the first optical band pass filter and for combining the same with the optical signals within optical wavelength channels within the add-drop wavelength band received from the output port of the multiplexing device,
wherein the add-drop wavelength bands for a set of different nodes are different and
wherein the multiplexing and demultiplexing devices for a same set of different nodes are identical,
wherein at different nodes a signal within a different wavelength channel is directed toward a same output port of the identical devices.
In accordance with another aspect of the invention there is provided a method of demultiplexing channelised optical signals comprising the steps of providing
an optical signal including signals in several of a plurality of non-overlapping wavelength bands within an application wavelength window;
filtering the optical signal to separate a second optical signal including optical signals within a first single non-overlapping wavelength band and separate a third optical signal including optical signals within a second non-overlapping wavelength band;
providing the second optical signal to a first optical demultiplexer;
demultiplexing the second optical signal into a plurality of channelised signals within the first non-overlapping wavelength band;
providing the third optical signal to a second optical demultiplexer identical to the first optical demultiplexer; and
demultiplexing the third optical signal into a plurality of channelised signals within the second non-overlapping wavelength band.
In accordance with the invention there is also provided an optical device for use in an optical network supporting optical communication within an application wavelength window comprising:
a first port for receiving a multiplexed optical signal including optical signals within each of a plurality of wavelength channels having a predetermined channel spacing within any one of
a plurality of non-overlapping wavelength bands;
a plurality of second ports; and
a wavelength dispersive element for separating the multiplexed optical signal received at the first port in dependence upon wavelength to provide a channelised signal to each of the plurality of second ports,
wherein the wavelength dispersive element has a periodic wavelength response having a free spectral range less than or equal to half of the application wavelength window such that a first optical device is for use within a system for at least one of multiplexing and demultiplexing channelised optical signals within a first non-overlapping band within the application wavelength window and a second identical optical device is for use within a system for at least one of multiplexing and demultiplexing channelised optical signals within a second different non-overlapping band within the application wavelength window.